Reactive silica powder



2,705,222 Patented Mar. 29, 1955 REACTIVE SILICA POWDER George H.Wagner, Kenmore, N. Y., assignor, by mesne assignments, to Union Carbideand Carbon Corporation, a corporation of New York No Drawing.Application November 6, 1948, Serial No. 58,809

4 Claims. (Cl. 252-488) This invention relates to a silica powder whichhas a chemically reactive surface, to a method of making such powder,and to chemical reactions employing such powder.

Finely-divided silica having an extensive surface area per unit weightmay be manufactured by the combustion of silicon compounds, such assilicon tetrachloride, tetraethyl silicate, or a chlorosilane. Theresulting product is useful as a filler or thickening agent but stillexhibits the chemical inertness typical of silicon dioxide. In addition,such silica powders are readily wet by water which leads to instabilityof greases and the like containing the powders as thickening agents.When employed as fillers in rubber and other elastomers, the presentsilica powders do not modify the elastorner chemically.

According to this invention, a silica powder having an extensive surfacearea per unit weight is treated with a chlorosilane of the groupconsisting of trichlorosilane, HSiCl3, and dichlorosilane, H2SiClz. As aresult of the treatment, the silica becomes coated with the hydrolysisproduct of the chlorosilane used. The water required for the hydrolysismay be present as absorbent moisture in the silica, as water vapor inthe atmosphere, or water may be added when relatively large amounts ofthe chlorosilanes in relation to the silica powder are used. The coatingof the hydrolysis product adheres firmly to the silica particles, andgives the silica a chemically reactvie, water-repellent surface.

The chemical reactivity of this surface may be ascribed to the presenceof silanic hydrogen in the coating, as the hydrolysis product oftrichlorosilane is silicon oxyhydride, (HSlO3/2)n, and the hydrolysisproduct of di chlorosilane is silicon oxydihydride, (H2Sl0)n. The coatedsilica powder is a strong reducing agent, and it will reduce silversalts to the metal. Active silver catalysts supported on silica may beprepared in this manner. The coated silica powder will react withcaustic soda and other alkaline materials to release hydrogen. Thecoated silica powder will also react with olefinic double bonds. Thus,it may be used as a cross-linking agent and filler in the vulcanizationof rubber and polymers and copolymers of butadiene and other diolefines.The coated silica powder may also serve as a stabilizer in vinylchloride resins to inhibit the release of hydrogen chloride from theseresins on heating.

The amount of chlorosilane hydrolysis product formed on the silicapowder bears a close relation to the amount of chlorosilane employeduntil the thickness of the coating approximately corresponds to amonomolecular layer of the hydrolysis product. This relationship wasshown by treating 100 grams of a silica powder obtained by a combustionprocess and having a surface area of 300 sq. meters/ gram with variousamounts of trichlorosilane together with about the theoretical amountsof water required in each case for complete hydrolysis of thetrichlorosilane (HSiCla) to silicon oxyhydride, (HSlO3/2)n, allowing forthe presence of one gram of water in the silica used. It is calculatedthat such silica powder containing about 16.6% silicon oxyhydride basedon the total composition would contain a monomolecular layer of thesilicon oxyhydride. The results are shown below:

TABLE I Silica coated with silicon oxyhydride Amount of (HSlOa r) in 100gm. Silica Percent HSiOlu Added, Grains (grams) 5 535 ProductTheoretical Found While larger amounts of trichlorosilane can be usedthan required for the formation of an amount of silicon oxyhydridecalculated to correspond to a monomolecular layer, there'is littleadvantage in using such large amounts because (1) a silica surfacehaving a monomolecular layer of silicon oxyhydride has probably attainedits maximum chemical reactivity and (2) such surfaces have optimum waterrepellency. On the other hand, waterrepellent coated silica may beobtained by employing smaller amounts of trichlorosilane than requiredfor the formation of a monomolecular layer of silicon oxyhydride on thesilica. This is shown in the table below, wherein the degree of waterrepellency of silica (surface area-300 sq. meters/gin.) coated withvarious amounts of silicon oxyhydride was determined by adding about0.05 gram of the coated silica to a oneounce bottle one-half filled withdistilled water. The bottles were shaken once a day and inspectedperiodically to determine the amount of material floating.

TABLE II Water repellency of siliconpxyhydride coated silica Percent ofCoated Silica Floating After Time in Days Percent (HSiO3 z)n in SilicaProduct In general, therefore, the amount of silicon oxyhydride orsilicon oxydihydride hydrolysis product deposited on the silica may varyfrom 4 to 30% by weight, and the preferred range is 8 to 20%. The amountof hydrolysis product calculated to give a monomolecular layer will, ofcourse, increase with the fineness of the silica powder. By a silicapowder of extensive surface area per unit weight, we mean a silicapowder having a surface of the order of magnitude of 50 to 600 squaremeters per gram.

The increased water-repellency of the silicon oxyhydride coated silicais of considerable importance in the formulation of greases.Finely-divided silica is a useful thickening agent for mineral oils toform greases but the greases so made have inadequate resistance towater. To demonstrate the superiority of the coated silica for makingwater-resistant greases, two greases were prepared. One grease contained10% of an uncoated silica formed by a combustion process and 90% of anaphthenic base oil having a viscosity of 283 SUS at 100 F.; the othercontained the same amounts of coated silica 3 and oil, but the silicaused had been treated with HSi Cl3 so that it was coated with 8% ofsilicon oxyhydride. To 20 grams of each of these greases water was addedhot 25% KOH, and checked in several instances by combustion analysis forcarbon and hydrogen.

in increments of 1 ml., the grease being stirred for 120 A k seconds at150 R. P. M. after each increment. The first l ylamn Product greasecontaining the untreated silica broke down 1n struc-. InitialPercentture after 7 ml. of water had been added; the second %gg%% Reactam 2%?ligi ag grease absorbed 20 ml. of water without change instrucowlglqride olefins g P t P t penency ture. In 102 rs. erccn ercenSilica coated with silicon oxyhydride or silicon oxy- Used H8101" RS101"dihydride readily reacts at elevated temperatures, for 1n- 1 y daysstance from 150 to 500 C. with olefinlc hydrocarbons, such as ethylene,propylene, butylene, pentene, octene, 0 Ethylenequ 4 0 O 0 cyclohexene,or butadiene to form additlon products s.1 None 8.1 0 100 b 65 whereinthe olefin is firmly bonded to the oxyhydrlde or 10 0 5-6 8-5 100 95 9.0..-do 0.5 5.9 4.5 100 95 oxydihydrlde coating. The water repellency ofthe coated 5 M 15' 7 so 65 silica is increased by reaction with theolefin, butadiene 30 1 85 31 1 r88 3 O... being particularly effectivefor thls purpose. 8 cyclohexenez 5 5. 6 5 5 100 80 The followingexamples will serve to lllustrate the 0 Q75 100 75 practice of theinvention: 11.6 Butadieue..- 0.5 8.9 100 100 EXAMPLE 1.SILICA COATEDWITH SILICON OXY l See Table II. HYDRIDE b Extrapolated from Table II.

tBytfionggusggrfiamltlytsis, as product was too water-reppellent to beOne hundred (100) grams of finely-divided silica made We by a combustionprocess were placed in a wide mouth EXAMPLE -ggi'gg gfi gg g s iOXYDIHX' gallon jug and 8 cc. of water were added. (In addition to thisadded Water, a o t 1 Percent y Welght 1S 1101" In a similar manner asdescribed in Example 3, silica y Present on the slllca 1ttelfi) The 1was e coated with silicon oxydihydride prepared as in Example tumbled,and allowed to stand for 48 hours. Thlrty- 2 was reacted with ethyleneand butadiene at various temfour (34) cc. of SiI-ICls were added insmall portions peratures. The results are tabulated below:

Initial P Alkylation Product ercent by Reac- Weight of Reactant Temp.,tion Percent Water Silicon Oxy- Olefins C. Time, Wt. Per- Wt. Per-Repeliency B dihydride in Hrs. cent cent Silica Used HzSiO I (R):Si0 b 1Day 15 Days a See Table with tumbling so that the evolution of hydrogenchloride gas was at a steady slow rate as the silicon oxyhydride coatingwas formed. The product was spread to a A inch bed and allowed to standover night, open to the air. Analysis showed 14.35 percent siliconoxyhydride. A monomolecular layer in the case of this silica (surfacearea=300 sq. meters/gram) would be about 16.6%. The product was quitewater repellent.

EXAMPLE '2.-SILICA COATED \VITH SILICON OXY- DIHYDRIDE One hundred (100)grams of finely-divided silica made by a combustion process were placedin a gallon bottle to which 3 grams of water were added. After tumblingand aging overnight, the silica was placed in a 2-gallon vacuumdesiccator which was evacuated. About 8 cc. of SiHzClz was slowlyvaporized into the system, where it reacted with the water coated silicaover a two-hour period. Analysis for silanic hydrogen by measuring thevolume of hydrogen evolved upon treatment with 25% aqueous KOH showed6.4% by weight of silicon oxydihydride. The product was water repellent.

EXAMPLE 3.-ALKYLATION OF SILICON OXYHYDRIDE COATED SILICA Siliconoxyhydride coated silica, made as described in Example 1, was placed ina one-inch I. D. Pyrex glass tube and a number of olefins were passedupwards through the silica bed at a temperature of 450 C. and atatmospheric pressure. Nitrogen gas was employed as a carrier for theolefins boiling higher than ethylene. The results are tabulated below,the amount of added oilefine being calculated as RSiOs 2 where R is thealkyl radical corresponding to the olefin. The analyses for uureactedsilanic hydrogen were made by reaction with It will be noted thatalkylation increases the waterrepellency of silicon oxydihydride coatedsilica to a greater degree than does alkylation of silicon oxyhydridecoated silica. In both instances, however, the alkylated products may besaid to possess a high degree of water repellency.

This application is in part a continuation of my copending applicationSerial No. 750,871 filed May 27, 1947, now abandoned.

What is claimed is:

1. A silica powder of extensive surface area per unit weight in whichthe surface of the silica is bonded to a reactive coating of a siliconhydride of the group consisting of silicon oxyhydride and siliconoxydihydride, the

' amount of said reactive coating being from 8% to 20% of the totalcomposition, said reactive coating being formed on the surface of thesilica by the hydrolysis respectively of one of the group consisting oftrichlorosilane and dichlorosilane.

2. A silica powder of extensive surface area per unit weight in whichthe surface of the silica is coated with 8 to 20% by weight of the totalcomposition of silicon oxyhydride, said silicon oxyhydride being formedon the surface of the silica by the hydrolysis of trichlorosilane.

3. A silica powder of extensive surface area per unit weight in whichthe surface of the silica is coated with 8 to 20% by weight of the totalcomposition of silicon oxydihydride, said silicon oxydihydride beingformed on title surface of the silica by the hydrolysis of dichloros1ane.

4. A silica powder of extensive surface area per unit weight in whichthe surface of the silica is bonded to a reactive coating consisting ofsilicon oxyhydride, the amount of such coating being approximately equalto a mon molecular layer of silicon oxyhydride on the surface of thesilica particles, said silicon oxyhydride being formed on the surface ofthe silica by the hydrolysis of trichloro- 6 Kistler Mar. 18, 1952Watson Apr. 15, 1952 FOREIGN PATENTS Great Britain Oct. 18, 1926Australia Feb. 4, 1943 OTHER REFERENCES Mellor: Comprehensive Treatiseon Inorganic and 10 Theoretical Chemistry, vol. 6, pp. 228429, N. Y.,

Longmans Green and Co., 1925. Copy in Div. 59.

Rochow: Chemistry of the Silicones, pages 5, 8, 16,

42, and 87. (Copy in Div. 64.)

1. A SILICA POWDER OF EXTENSIVE SURFACE AREA PER UNIT WEIGHT IN WHICHTHE SURFACE OF THE SILICA IS BONDED TO A REACTIVE COATING OF A SILICONHYDRIDE OF THE GROUP CONSISTING OF SILICON OXYHYDRIDE AND SILICONOXYDIHYDRIDE, THE AMOUNT OF SAID REACTIVE COATING BEING FROM 8% TO 20%OF THE TOTAL COMPOSITION, SAID REACTIVE COATING BEING FORMED ON THESURFACE OF THE SILICA BY THE HYDROLYSIS RESPECTIVELY OF ONE OF THE GROUPCONSISTING OF TRICHLORO SILANE AND DICHLOROSILANE.